Owing to the depletion of fossil petroleum fuels and their associated environmental polluting effects, research is being focused recently on renewable green alternative plant-derived fuels. Biodiesel is one such alternative for diesel fuels which is non-toxic, eco-friendly and biodegradable renewable fuel. Biodiesel can be prepared from vegetable oils (or) animal fats (or) cooked oils which are largely composed of C14-C20 fatty acid triglycerides.
A century ago, Rudolf Diesel directly tried peanut oil as transport fuel before the petroleum fuels came in to the market. The paper titled “Biodiesel production: a review1” by Fangrui Ma et. al. in Bioresource Technology, 70 (1999) 1-15, discussed the drawbacks of triglycerides as direct fuels. They reported that some modification processes like blending, microemulsion, thermal cracking (pyrolysis) and transesterification (alcoholysis) are needed to convert oils to transport fuels. Compared to other processes transesterification has many advantages and commonly used for biodiesel production.
Transesterification of triglycerides with short-chain alcohols gives biodiesel. Normally methanol is used because of its high reaction rate, low cost and abundantly available. The paper titled “Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters” by Gerhard Knothe in Fuel Processing Technology, 86 (2005) 1059-1070, discussed the variations in the properties of different fatty acid alkyl esters. They suggested that isopropyl esters have better fuel properties than methyl esters; but the cost of iso-propanol is the main disadvantage compared to methanol.
Transesterification reaction is generally carried out by using acid (or) base (or) enzyme catalysts (or) supercritical alcohol conditions. As per the paper titled “Biodiesel Fuel Production by Transesterification of Oils” by Hideki Fukuda et. al. in Journal of Bioscience and Bioengineering, Vol. 92, No. 5 (2001) 405-416, the acid catalyzed transesterification has slow reaction rate. Enzymes catalysis is time consuming and very high in cost than alkali and their activities are relatively low. The use of supercritical methanol requires high temperature of more than 350° C., high pressure of 45 MPa and high methanol amount in catalyst free conditions. Based on this knowledge, base catalyzed transesterification is considered suitable for industrial process.
Currently, in industry homogeneous base catalysts such as NaOH and KOH are used for the biodiesel production. The paper titled “Heterogeneous Base Catalysts for Transesterification in Biodiesel Synthesis” by Dae-Won Lee et. al. in Catalysis Surveys from Asia, 13 (2009) 63-77, discussed the drawbacks of homogeneous catalysts such as corrosion, catalyst recovery and limitation in continuous process. Further, they have also reported the hurdles/problems such as high reaction temperature (100-250° C.), catalyst amount (3-10 wt %), methanol:oil ratio (10:1-25:1) while using heterogeneous catalysts.
Layered double hydroxides (LDHs; otherwise referred as hydrotalcite-like [HT-like] materials) both in their as-synthesized and heat-treated forms are categorized as heterogeneous base catalysts and can be used for various base catalyzed reactions because of their tunable basicity. There are several reports using heat-treated LDHs as catalysts for biodiesel production.
The paper entitled “Structure-reactivity correlations in MgAl hydrotalcite catalysts for biodiesel synthesis” by David G. Cantrell et. al. in Applied Catalysis A: General, 287 (2005) 183-190, revealed the biodiesel synthesis from glyceryl tributyrate with methanol. The authors reported both the conversion of glyceryl tributyrate and the yields of methyl butanoate, diglycerides and monoglycerides. They concluded that compared to MgO, oxides derived from MgAl hydrotalcites has higher activity for this reaction. However, the calcination of hydrotalcite (HT) under nitrogen flow and use of high methanol amount are the main drawbacks for this report.
The paper titled “Calcined Mg—Al hydrotalcites as solid base catalysts for methanolysis of soybean oil” by Wenlei Xie et. al. in Journal of Molecular Catalysis A: Chemical, 246 (2006) 24-32, reported 67% yield of biodiesel with the methanol:oil ratio of 15:1 in 9 h with 7.5 wt % catalyst under refluxing conditions. The drawbacks of this method are high methanol:oil ratio, longer reaction time, relatively lesser yield of biodiesel and fail to address the reusability of the catalyst.
The paper titled “Biodiesel production from soybean oil using calcined Li—Al layered double hydroxides catalysts” by J. Link Shumaker et. al. in Catalysis Letters, Vol. 115, No. 1-2 (2007) 56-61, reports >80% yield of biodiesel using 15:1 methanol:oil ratio and 3 wt % catalyst at reflux temperature in 1 h. Here again the yield is lesser even at high methanol:oil ratio and using more expensive lithium.
The paper entitled “Transesterification of poultry fat with methanol using Mg—Al hydrotalcite derived catalysts” by Yijun Liu et. al. in Applied Catalysis A: General, 331 (2007) 138-148, discussed the catalysis of both calcined and rehydrated HT-like catalysts for biodiesel synthesis from poultry fats. A maximum conversion of 93% at 120° C. with 30:1 methanol:oil ratio and 10 wt % of catalyst in 8 h was reported. The main drawbacks are process intense variables like heating under inert conditions, high reaction temperature, high catalyst amount and longer time.
The paper titled “Transesterification Catalysts from Iron Doped Hydrotalcite-like Precursors: Solid Bases for Biodiesel Production” by Gerald S. Macala et. al. in Catalysis Letters, 122 (2008) 205-209, discussed the transesterification of triacetin as well as soybean oil with doped HT-like materials. The 10% Fe-doped hydrotalcite gave 38% of yield of biodiesel after 1 h at 80° C. and 1 wt % catalyst for soybean oil. Their main drawback is the poor activity of the regenerated catalyst.
The paper titled “Biodiesel synthesis using calcined layered double hydroxide catalysts” by J. Link Shumaker et. al. in Applied Catalysis B: Environmental, 82 (2008) 120-130, reported the biodiesel synthesis from glyceryl tributyrate and soybean oil with methanol over different oxides derived from LDHs. They used high methanol:oil ratio of 15:1 with the oxides Mg—Al, Mg—Fe and Li—Al at reflux temperature and among them Li—Al oxides showed better activity than other oxides. But poor stability of these catalysts is a major drawback for them to be practiced in industrial operations.
The paper titled “Metal-Loaded MgAl Oxides for Transesterification of Glyceryl Tributyrate and Palm Oil” by T. Tittabut et. al. in Industrial & Engineering Chemistry Research, 47, (2008) 2176-2181, reported the transesterification of glyceryl tributyrate and palm oil with methanol. 96% ester content and 87% yield of biodiesel was reported with the methanol:oil molar ratio of 45:1 at 100° C., 8 wt % catalyst and 9 h reaction time for K loaded MgAl hydrotalcite. The main drawback for this process is the longer time needed for calcination (35 h). The authors reported the recalcination followed by reload of the metal is the way to do the recycle experiment, an energy intensive multi-step operation.
The paper titled “MgCoAl-LDH derived heterogeneous catalysts for the ethanol transesterification of canola oil to biodiesel” by Eugena Li et. al. in Applied Catalysis B: Environmental, 88 (2009) 42-49, reported ethanol transesterification of canola oil with calcined MgCoAl and MgCoAlLa containing LDHs. A maximum yield of 96-97% at 200° C. using 16:1 of ethanol:oil ratio in 5 h was reported. High temperature and alcohol:oil molar ratio are their drawback.
The paper entitled “Transesterification of Rice Bran Oil with Methanol Catalyzed by Mg(Al)La Hydrotalcites and Metal/MgAl Oxides” by Pacharaporn Chuayplod et. al. in Industrial & Engineering Chemistry Research, 48 (2009) 4177-4183, reported two-step catalyzed process such as esterification and subsequent transesterification due to the high FFA content in rice bran oil. They reported 97% ester content and 78% yield for the product with rehydrated MgAlLa hydrotalcite at 100° C., 30:1 methanol:oil ratio, 7.5 wt % catalyst and reaction time of 9 h. Their main drawback is the time taken for Mg(Al)La oxide preparation (35 h) and rehydration under nitrogen for 24 h. During reusability tremendous decrease in the yield of biodiesel was noted compared to original catalyst. In order to get the good results, authors suggested the requirement of time-consuming recalcination followed by rehydration process before every cycle.
The paper entitled “Biodiesel Production from Waste Oil Using Mg—Al Layered Double Hydroxide Catalysts” by A. Brito et. al. in Energy Fuels, 23 (2009) 2952-2958, reported the biodiesel production from sunflower oil and waste oil. They reported the high yield in the temperature range of 120-160° C., methanol:oil ratio of 24:1, 6 wt % catalyst and 6 h reaction time. Their main drawback is intense process variables.
The paper titled “Synthesis, characterization, and activity in transesterification of mesoporous Mg—Al mixed-metal oxides” by Jonggol Tantirungrotechai et. al. in Microporous and Mesoporous Materials, 128 (2010) 41-47, reported transesterification of soybean using some series of metal impregnated MgAl mixed oxides. They reported >90% yield of biodiesel with methanol:oil ratio of 20:1 at 70° C., 5 wt % catalyst and the reaction time of 8 h. Their main drawbacks are the complicated material synthesis and high methanol amount. They have used high oxygen flow for calcination and carried out overnight drying before the use. Further, the recyclability of the catalysts is not addressed.
The paper entitled “Base Catalysts Derived from Hydrocalumite for the Transesterification of Sunflower Oil” by Maria Jose Campos-Molina et. al. in Energy Fuels, 24 (2010) 979-984, discussed the catalysis of calcined hydrocalumite for biodiesel production. They reported the 97% yield of biodiesel with 12:1 methanol:oil ratio at 60° C., 1 wt % catalyst and the reaction time of 3 h. The main drawbacks are, resource intense material synthesis (use of ethanol), longer period of activation (13 h) and necessity of preactivation under inert atmosphere, process intense reaction conditions (inert conditions, high methanol:oil ratio) and not reusable for multiple cycles (could do only for two cycles after which the catalyst could not be recovered).
The paper entitled “Biodiesel from palm oil via loading KF/Ca—Al hydrotalcite catalyst” by Lijing Gao et. al. in Biomass and Bioenergy 34 (2010) 1283-1288 reported the biodiesel production from palm oil using KF/Ca—Al catalyst. The yield of FAME increased with an increase in KF loading and in shorter reaction time. The optimized methanol:oil ratio is 12:1. They recycled the catalyst only for two cycles. The use of expensive KF as an additional reagent and sensitive and time consuming synthetic protocol of the catalyst are the main drawbacks.
The patent (CN 101608131 A) entitled “Method of manufacturing bio-diesel oil without glycerol byproduct” by Zhong Xin et. al. reported that the biodiesel manufacture from vegetable oils and animal fats without glycerol as byproduct. They used alcohol:oil ratio of 1-30:1 at 30-450° C., 0.05-30 MPa for 2-18 h with variety of solid acid/base catalysts and organic base catalysts along with different transesterifying agents like dimethyl carbonate, diethyl carbonate etc. Their main drawback is that the reaction is carried out under high pressures and the usage of costly chemicals.
The patent (WO 2010/112641 A1) entitled “Method for the production of biofuels by heterogeneous catalysis employing a metal zincate as precursor of solid catalysts” by Pedro Jesus Maireles Torres et. al. reported the transesterification of vegetable (or) animal oils or fats for the biodiesel production using calcined zincate of an alk. earth metal (or) of a divalent transition metal. Their main drawbacks are the pre-activation, higher methanol:oil ratio and necessity of inert reaction atmosphere.
The Patent (CN 101559359 A) entitled “Solid base catalyst for preparation of biodiesel by transesterification and its preparation” by Hui Wang et. al. reported the biodiesel preparation from trioleic acid glyceryl ester using KOH treated CaO—ZrO2 at 140-180° C. for 4-6 h. Their main drawbacks are the time consuming preparation of the expensive catalysts and higher reaction temperatures.
The Patent (CN 101314131 A) entitled “Method for preparing modified hydrotalcite solid base catalyst for preparation of biodiesel” by Guomin Xiao et. al. reported the modified hydrotalcite for biodiesel preparation. Their main drawbacks are chemicals demanding and time consuming process to obtain the active catalyst.
The Patent (CN 1824735 A) entitled “Method for preparing biological diesel fuel from Jatropha curcas oil using solid catalyst” by Hang Yin et. al. reported the biodiesel preparation from jatropha oil using org. salt of alkali metal and/or alk. earth metal (lithium formate, sodium propionate, etc) and carrier (Al2O3, NaY zeolite, etc) as solid catalyst. Their main drawbacks are the use of expensive chemicals for catalyst preparation and pressure required (0.9 to 1.5 MPa) for the calcination and as well for the reaction.
The patent (U.S. Pat. No. 7,420,073 B2) entitled “Process for the alcoholysis of acid oils of vegetable or animal origin” by Gerard Hillion et. al. reported the biodiesel production using zinc aluminate as catalyst. Their main drawbacks are the high temperature range (180 to 210° C.) and high pressures (4 to 6 MPa).
The Patent (CN 101358141 A) entitled “Method for preparing biodiesel oil from idesia polycarpa maxim. var. vestita diels oil by using solid alkali catalyst” by Hang Song et. al. reported that Mg—Al composite oxide as catalyst for biodiesel preparation. The main drawbacks are the multi-step time consuming process and requirement of many additional chemicals.
The Patent (CN 101294094 A) entitled “Method for producing bio-diesel oil using nanoscale solid heteropoly acid or heteropoly base catalyst” by Heyou Han et. al. reported that biodiesel production using nanoscale solid heteropoly acid (or) heteropoly base catalyst with alcohol:oil ratio of 6-48:1 at 60-90° C. in normal pressure for 1-10 h and 1-6 wt % of catalysts. Heteropoly acid/base catalysts are generally expensive.
The patent (U.S. Pat. No. 7,563,915 B2) entitled “Green biodiesel” by Jack Vincent Matson et. al. reported that solid base catalysts such as simple metal oxides, mixed metal oxides, hydrotalcites and silicates for biodiesel manufacture. They discussed the transesterification of vegetable oil with alcohols (methanol, ethanol) at 60-450° C., 1-500 atmospheres for 5-60 min. Their main drawbacks are the high methanol:oil ratio and high preferred temperature range of 150-260° C.
The Patent (CN 101249449 A) entitled “Preparation and application of new-type solid base catalyst for synthesis of bio-diesel fuel” by Jianguo Yang et. al. reported that the potassium fluoride on different supports like alumina, calcia, dolomite etc. as solid base catalyst for biodiesel synthesis. They used plant oil, animal fat (or) waste oil with low-carbon alcohols (methanol, ethanol, propanol [or] butanol) with different ratios at 50-110° C. for 1-3 h. Such catalysts are generally prone for leaching and fluoride leaching may cause separation/contamination issues.
The Patent (CN 101185903 A) entitled “Manufacture and application of solid base catalyst for synthesizing bio-diesel oil” by Guosheng Zheng et. al. reported that calcium methoxide as catalyst for biodiesel synthesis using animal and vegetable oil with methanol. Calcium methoxide was prepared by firing calcium salts at desired temperature and then cooling with methanol (or) methanolic steam. Their main drawback is the process intense synthesis of catalyst along with likelihood of leaching of calcium.
The Patent (CN 101113349 A) entitled “Production of bio-diesel with convenient post-treatment by esterification of vegetable oil” by Tianbo Weng reported activated magnesium oxide as a catalyst for biodiesel synthesis. He has carried out the transesterification of vegetable oil with alcohols (methanol, ethanol [or] n-butanol) at a ratio of 4-25:1 in the presence of different wt % (0.01-3%) of the catalysts. The main drawbacks are the time consuming procedures to recover the biodiesel and glycerol.
The Patent (WO 2006/050925 A1) entitled “Process for producing esters from vegetable oils or animal fats using heterogeneous catalysts” by Dante Siano et. al. reported that magnesium oxide and magnesium-aluminum mixed oxides derived from hydrotalcite as catalysts for biodiesel production. They used alcohol:oil ratio of 4 to 30:1 at 100 to 250° C. Their main drawback is the high temperature used for this reaction.
The Patent (CN 101024189 A) entitled “Preparation and application of magnetic solid base catalyst for preparation of bio-diesel fuel by transesterification” by Xiaoyong Lu et. al. reported that mixture of different wt % of magnetic material, metal oxide/salt with alkali metal salt as catalyst for biodiesel preparation. They have carried out transesterification reaction for different oils. Their main drawback is the requirement of time consuming preparation of the magnetically separable costlier catalyst.
The Patent (CN 1891786 A) entitled “Production technology of bio-diesel fuel from tallowseed oil” by Yinyu Gao et. al. reported the biodiesel production using alkali, acid, enzyme and solid magnetic catalysts. They have carried out the transesterification of tallowseed oil with lower alcohols at 20-120° C. for 0.5-24 h with 0.1-10 wt % of catalysts. Their main drawback is the use of homogeneous catalysts such as alkali and acids which are making the process as non-ecofriendly. The usage of enzyme is time consuming and expensive.
The Patent (WO 2006/043281 A1) entitled “Improved process for the preparation of fatty acid methyl ester (biodiesel) from triglyceride oil through tranesterification” by Pushpito Kumar Ghosh et. al. reported the biodiesel preparation from Jatropha curcus oil using methanolic-KOH solution. The main drawback is the use of corrosive non-reusable alkali-based homogeneous catalyst and associated post-operative clean up.
The patent (U.S. Pat. No. 7,151,187 B2) entitled “Process for transesterification of vegetable oils or animal oils by means of heterogeneous catalysts based on zinc or bismuth, titanium and aluminum” by Bruno Delfort et. al. reported the biodiesel production using heterogeneous catalysts. Their main drawbacks are the usage of high methanol amount and high reaction temperature (200° C.).